This is a (multiple allowed):

• bug

• enhancement

• feature-discussion (RFC)

• CakePHP Version: 4.2.4

• Platform and Target: PHP 7.4.12, MacOS 10.15.7

What you did

Trying to patch/save a belongs to many association data when a primary key is non-standard (in the sense that I have a composite pk) doesn't work.

#PostsTable
'belongsToMany' => [
    'Tags' => [
        'through' => 'PostsTags',
    ],
],

#PostsTagsTable
public function initialize(array $config): void
{
    $this->setPrimaryKey(['post_id', 'tag_id', 'primary']);
}

#Save function in PostsTable
$tags = [
    [
        'id' => 123,
        '_joinData' => ['primary' => 1],
    ],
];
$post = $this->get(155);
$this->patchEntity($post, compact('tags'));
$this->save($post);

What happened

Cannot insert row, some of the primary key values are missing. Got (155, 123, ), expecting (post_id, tag_id, primary)

What you expected to happen

I should be able to patch the $post and have it save the Tags association. This is working for me in my old Cake 3.3 project. I've tried debugging on my own but I don't know where the marshaller is going wrong or if the shape of my data is wrong.